Assessment and Cleanup Options

Assessment

SCE&G's investigation activities of the Congaree River consisted of 5 phases of preliminary surveys and sampling from September 2010 through March 2012. A total of 244 sediment and soil samples were collected to determine the depth and extent of the tar-like material (TLM). Of the samples collected, 40 were sent to a laboratory to be further analyzed. The analytical results indicated the presence of some volatile organic compounds (VOCs) in the samples. The dominant group of semi-volatile organic compounds (SVOCs) detected were polynuclear aromatic hydrocarbons (PAHs). The sediment layer containing TLM varies from approximately less than 1 inch in thickness to at least 1 foot. Water samples from the river were also collected and have been analyzed. The water samples have shown no tar-related chemicals of concern.

The map below shows the sampling points and grid lines used in the assessment of the affected area of the Congaree River.

Cleanup Alternatives

Based on the site assessment and potential exposure risk from direct skin contact with the tar-like material (TLM), further action is justified in the affected area of the river to protect human health and the environment. Four cleanup alternatives for the sediments and soils have been evaluated based on the following seven criteria:

Protection of human health and the environment,

Compliance with state and federal regulations,

Reduction of contamination mass, volume and toxicity,

Short-term effectiveness,

Long-term effectiveness,

Implementability, and

Cost.

Table 1 below describes each cleanup alternative and its estimated cost. Table 2 shows a comparison of the four alternatives based on the seven criteria.

Table 1 - Cleanup Alternatives Evaluated by DHEC & Estimated Cost

1. No Action – Leave the TLM in place. This option is primarily used as a baseline for comparison with other options.

Estimated Cost: $0.00

2. Monitoring and Institutional Controls – Leave the TLM in place and restrict access to the area by placing signs in and along the river and installing a chain link fence along the eastern shoreline. 30-year annual monitoring of sediment conditions in and downstream of the affected area would be performed to detect any movement of the TLM.

Estimated Cost: $677,000.00

3. Sediment Capping and Institutional Controls – Leave the TLM in place and "cap" it with a physical barrier on top of the sediment. The barrier would be designed to withstand routine flooding and would most likely include a geotextile fabric overlaid by riprap stone. Institutional controls and monitoring similar to Alternative 2 would be included.

Estimated Cost: $7,681,000.00

4. Removal of the TLM and Impacted Sediments – Physically remove the TLM from the river. This option would include construction of a temporary dam and dewatering of the affected area so that the TLM and sediments could be removed and taken to a licensed off-site facility for disposal. The ecological environment would be restored upon completion.